1. Field of the Invention
The present invention relates to coil apparatuses capable of serving as transformers and choke coils and a method for manufacturing the same.
2. Description of the Related Art
FIG. 7A is an exploded view of a coil apparatus. FIG. 7B is a sectional view taken along line 7Bxe2x80x947B of the coil apparatus shown in FIG. 7A. A coil apparatus 1 shown in FIGS. 7A and 7B is incorporated in a circuit such as a DC-to-DC converter, and serves as a transformer or a choke coil. The coil apparatus 1 includes an electronic-part-mounting substrate 2, a coil pattern group 3 formed on the electronic-part-mounting substrate 2, a pair of core members 4(4a) and 4(4b), and a core-coupling unit 5xe2x80x2.
The electronic-part-mounting substrate 2 carries electronic parts for forming a circuit, and a circuit pattern is formed on the electronic-part-mounting substrate 2. The electronic-part-mounting substrate 2 is a multi-layered substrate including a plurality of substrate elements laminated on each other. For example, the plurality of substrate elements may be individually provided with coil patterns 7 which are disposed coaxially with each other, the coil patterns 7 forming the coil pattern group 3. When the coil apparatus 1 is used as a transformer apparatus, at least one of the coil patterns 7 serves as a primary coil and the remainder serves as a secondary coil.
The pair of core members 4(4a) and 4(4b) shown in FIGS. 7A and 7B are made of a powdered magnetic material such as a ferrite by sintering. The core members 4(4a) and 4(4b) are E-type core members which individually include planar top plates 8, each top plate 8 being provided with core-legs 9(9a), 9(9b), and 9(9c) projecting from one end, an intermediate part, and the other end, respectively, of the top plate 8, whereby the cross-section of each core member 4(4a) or 4(4b) is E-shaped.
The electronic-part-mounting substrate 2 is provided with core-leg-passing through-holes 10(10a), 10(10b), and 10(10c) in an outside part, a central part, and the opposite outside part, respectively, of the coil pattern group 3. As shown in FIG. 7B, the core-legs 9(9a), 9(9b), and 9(9c) of each core member 4(4a) or 4(4b) are inserted into the core-leg-passing through-holes 10(10a), 10(10b), and 10(10c), respectively, from the top or bottom side of the electronic-part-mounting substrate 2. The core-legs 9a, 9b, and 9c of the top core member 4(4a) come into contact with the respective core-legs 9(9a), 9(9b), and 9(9c) of the bottom core member 4(4b) at tips of the core-legs 9(9a), 9(9b), and 9(9c) of the respective core members 4(4a) and 4(4b).
The core-coupling unit 5xe2x80x2 receives and couples the pair of core members 4(4a) and 4(4b) with each other, as shown in FIG. 7B. The core-coupling unit 5xe2x80x2 is formed by bending a metallic plate, and includes a top plate 12, legs 13(13a) and 13(13b), and hooks 14(14a) and 14(14b). That is, the top plate 12 for covering the top plate 8 of the core member 4(4a) is bent in the standing direction of the core-legs 9(9a), 9(9b), and 9(9c) at the right and left ends of the top plate 12, thereby forming the legs 13(13a) and 13(13b), and the legs 13(13a) and 13(13b) are individually bent toward the inside at the ends thereof, thereby forming the hooks 14(14a) and 14(14b).
The distance between the top plate 12 and the hooks 14 is substantially the same as a distance h between an outer surface 8a of the top plate 8 of the top core member 4(4a) and the outer surface 8a of the top plate 8 of the bottom core member 4(4b) when the core-legs 9(9a), 9(9b), and 9(9c) of the top core member 4(4a) are in contact with the respective core-legs 9(9a), 9(9b), and 9(9c) of the bottom core member 4(4b) at tips of the core-legs 9(9a), 9(9b), and 9(9c) of the core members 4(4a) and 4(4b), as shown in FIG. 7B. As shown in FIG. 7B, the core-coupling unit 5xe2x80x2 couples the core members 4(4a) and 4(4b) with each other, the core-legs 9(9a), 9(9b), and 9(9c) of the respective core members 4(4a) and 4(4b) being in contact with each other at the tips of the core-legs 9(9a), 9(9b), and 9(9c), so that the core members 4(4a) and 4(4b) are clamped at the left and right ends thereof by the top plate 12 and the hooks 14(14a) and 14(14b), respectively. The core members 4(4a) and 4(4b) are coupled with each other so as to be movable relative to each other in directions xe2x88x9d (backward and forward) shown in FIG. 7A. A width W in the backward and forward directions of each core-leg-passing through-hole 10(10a), 10(10b), or 10(10c) is set greater than a width w of each core-leg 9(9a), 9(9b), or 9(9c) of the core member 4(4a) or 4(4b) so that the core members 4(4a) and 4(4b) can move backward and forward.
The coil apparatus shown in FIGS. 7A and 7B is formed, for example, as described below. The core members 4(4a) and 4(4b) are disposed at the top and bottom sides, respectively, of the electronic-part-mounting substrate 2 provided with the coil pattern group 3 and the core-leg-passing through-holes 10(10a), 10(10b), and 10(10c). The core-legs 9(9a), 9(9b), and 9(9c) of the top core member 4(4a) are inserted into the corresponding core-leg-passing through-holes 10(10a), 10(10b), and 10(10c), respectively, of the electronic-part-mounting substrate 2 from the topside thereof, and the core-legs 9(9a), 9(9b), and 9(9c) of the bottom core member 4(4b) are inserted into the corresponding core-leg-passing through-holes 10(10a), 10(10b), and 10(10c), respectively, of the electronic-part-mounting substrate 2 from the bottom side thereof, so that the core-legs 9(9a), 9(9b), and 9(9c) of the respective top and bottom core members 4(4a) and 4(4b) come into contact with each other at the tips thereof.
The legs 13(13a) and 13(13b) of the core-coupling unit 5xe2x80x2 are inserted, from the top of the core members 4(4a) and 4(4b) coupled with each other so that the respective core-legs 9(9a), 9(9b), and 9(9c) are in contact with each other at the tips thereof, into the left core-leg-passing through-hole 10(10a) at the outer side of the core-leg 9(9a) and the right core-leg-passing through-hole 10(10c) at the other outer side of the core-leg 9(9c), respectively.
The core-coupling unit 5xe2x80x2 thus coupling the core members 4(4a) and 4(4b) with each other is incorporated into the electronic-part-mounting substrate 2. That is, the core members 4(4a) and 4(4b), by being thus incorporated into the electronic-part-mounting substrate 2, are mounted on the coil pattern group 3 in such a manner that the core members 4(4a) and 4(4b) clamp the electronic-part-mounting substrate 2 at a part of the coil pattern group 3 from the top and bottom sides of the electronic-part-mounting substrate 2.
Then, the coupled core members 4(4a) and 4(4b) are slid backward and forward relative to each other, so as to rub against each other at a contact part between the core members 4(4a) and 4(4b), that is, at the tips of the core-legs 9(9a), 9(9b), and 9(9c) of the respective core members 4(4a) and 4(4b). By thus rubbing the tips of the core-legs 9(9a), 9(9b), and 9(9c) with each other (by performing core-rubbing), an effect described below can be obtained.
As described above, since the core members 4(4a) and 4(4b) are made by sintering a powdered magnetic material, the tips of the core-legs 9(9a), 9(9b), and 9(9c) of the core members 4(4a) and 4(4b) are initially coarse. Moreover, when coupling the core members 4(4a) and 4(4b) with each other, dust is received between the core-legs 9(9a), 9(9b), and 9(9c) of the core members 4(4a) and the core-legs 9(9a), 9(9b), and 9(9c) of the core members 4(4b). Therefore, the tips of the core-legs 9(9a), 9(9b), and 9(9c), when coupled, are not in close contact with each other. By performing core-rubbing, the tips of the core-legs 9(9a), 9(9b), and 9(9c) become substantially mirror-finished, and the dust received between the core-legs 9(9a), 9(9b), and 9(9c) is removed, whereby the tips of the core-legs 9(9a), 9(9b), and 9(9c) of the top core member 4(4a) and the tips of the core-legs 9(9a), 9(9b), and 9(9c) of the bottom core member 4(4b) are brought into close contact with each other. By thus bringing the core members 4(4a) and 4(4b) into close contact with each other, the inductance value can be prevented from decreasing and deterioration of the characteristics of the coil apparatus 1 can be avoided.
In the above known coil apparatus, the pair of core members 4(4a) and 4(4b) are firmly pressed and clamped by the core-coupling unit 5xe2x80x2 at the left and right ends of the top and bottom faces of the pair of core members 4(4a) and 4(4b). This causes a problem, in that the core members 4(4a) and 4(4b) do not move to slide on each other unless a large force is applied to the core members 4(4a) and 4(4b) when performing core-rubbing.
However, applying a large force when rubbing the core members 4(4a) and 4(4b) against each other causes a further problem. In order to reduce the thickness of the coil apparatus, in order to comply with recent requirements, it is desirable to reduce the thickness of the core members 4(4a) and 4(4b). When this is done, the core members 4(4a) and 4(4b) may be broken or cracked by the large applied force. Therefore, it has been difficult to reduce the thickness of the core members 4(4a) and 4(4b), which has made the reduction in thickness of the coil apparatus 1 more difficult.
In response to these problems, the present invention provides a coil apparatus and a method for manufacturing the same, in which core members can be reduced in thickness and easily rubbed against each other in the assembly process of the coil apparatus, and breakage of the core members is suppressed, whereby the coil apparatus can be reduced in thickness.
To these ends, according to an aspect of the present invention, a coil apparatus comprises a coil pattern group formed on an electronic-part-mounting substrate for mounting electronic parts; a pair of core members mounted on the coil pattern group in a manner such that the pair of core members clamp a part of the coil pattern group from the top and bottom sides of the electronic-part-mounting substrate; core-leg-passing through-holes formed in a region of the electronic-part-mounting substrate in which the coil pattern group is provided, the core-leg-passing through-holes being provided for receiving core-legs passing therethrough, the core-legs being provided on at least one of the pair of core members; and a core-coupling unit which clamps and couples the pair of core members with each other from the top and bottom sides of the electronic-part-mounting substrate by using the core-leg-passing through-holes. The core-coupling unit includes a top cover and a bottom cover each having a U-shape, the top cover and the bottom cover clamping the core members at the top and bottom sides of the core members between base plates of the respective U-shaped top cover and bottom cover with legs of the respective U-shaped top cover and bottom cover being coupled with each other. Portions of the top cover and the bottom cover define an anti-removal unit which maintains the legs of the respective top cover and bottom cover in a coupled state; a backward-forward-core-position-restricting unit which restricts the positions of the core members with respect to the respective top cover and bottom cover in the backward and forward directions; and a backward-forward-movement-allowing unit which allows backward and forward movement of the top cover and the bottom cover relative to each other when the core members are clamped between the top cover and the bottom cover, the legs of which are maintained in a coupled state by the anti-removal unit, and which moves the top core member and the top cover as a unit or the bottom core member and the bottom cover as another unit backward and forward relative to each other, the positions of the top core member and the bottom core member being individually restricted in the backward and forward directions with respect to the top cover and the bottom cover, respectively, by the backward-forward-core-position-restricting unit.
The anti-removal unit may be formed with apertures formed in first legs of one of the top cover and the bottom cover, the first legs being disposed outside second legs of the other one of the top cover and the bottom cover, and projections formed on the second legs of the other one of the top cover and the bottom cover, for anchoring at the corresponding apertures so as to prevent removal, the second legs being disposed inside the first legs of the one of the top cover and the bottom cover. The backward-forward-movement-allowing unit may be formed with play-gaps between each projection and respective front and rear edges of the aperture of the anti-removal unit.
The legs of at least one of the top cover and the bottom cover may be each provided with cut-away parts for providing relief at regions of the leg which come into contact with edges of the core-leg-passing through-hole when the one of the top cover and the bottom cover moves backward and forward. The projections of the anti-removal unit may each include inclined faces along which the edges of each aperture climb when the top cover and the bottom cover move backward and forward relative to each other.
The backward-forward-core-position-restricting unit may include lips which protrude in the thickness direction from front ends and rear ends, respectively, of the base plates and which anchor at front end-faces and rear end-faces, respectively, of the core members.
The coil apparatus according to the present invention may further comprise a fixing unit for fixing the core members either directly or indirectly via the core-coupling unit to the electronic-part-mounting substrate.
The fixing unit may comprise a bonding material made of a resin.
According to another aspect of the present invention, a method is provided for manufacturing a coil apparatus which comprises a coil pattern group formed on an electronic-part-mounting substrate for mounting electronic parts; a pair of core members mounted on the coil pattern group in a manner such that the pair of core members clamp a part of the coil pattern group from the top and bottom sides of the electronic-part-mounting substrate; core-leg-passing through-holes formed in a region of the electronic-part-mounting substrate in which the coil pattern group is provided, the core-leg-passing through-holes being provided for receiving core-legs passing therethrough, the core-legs being provided on at least one of the pair of core members; and a core-coupling unit which clamps and couples the pair of core members with each other from the top and bottom sides of the electronic-part-mounting substrate by using the core-leg-passing through-holes, wherein the core-coupling unit includes a top cover and a bottom cover each having a U-shape, the top cover and the bottom cover clamping the core members at the top and bottom sides of the core members between base plates of the respective U-shaped top cover and bottom cover with legs of the respective U-shaped top cover and bottom cover being coupled with each other, the core-coupling unit including an anti-removal unit which maintains the legs of the respective top cover and bottom cover in a coupled state; a backward-forward-core-position-restricting unit which restricts the positions of the core members with respect to the respective top cover and bottom cover in the backward and forward directions; and a backward-forward-movement-allowing unit which allows backward and forward movement of the top cover and the bottom cover relative to each other when the core members are clamped between the top cover and the bottom cover of which the legs are maintained in a coupled state by the anti-removal unit, and which moves the top core member and the top cover as a unit or the bottom core member and the bottom cover as another unit backward and forward relative to each other, the positions of the top core member and the bottom core member being individually restricted in the backward and forward directions with respect to the top cover and the bottom cover, respectively, by the backward-forward-core-position-restricting unit. The method comprises the steps of disposing the pair of core members at the top and bottom sides, respectively, of the electronic-part-mounting substrate; disposing the top cover of the core-coupling unit outside the top core member and the bottom cover of the core-coupling unit outside the bottom core member; mounting the pair of core members onto the coil pattern group, the pair of core members being coupled with each other by being clamped by the top cover and the bottom cover which are coupled with each other; and rubbing the top core member and the bottom core member against each other at the contact part therebetween by slidingly moving the top core member and the top cover as a unit or the bottom core member and the bottom cover as another unit relative to each other, thereby bringing the top core member and the bottom core member into close contact against each other.
The method for manufacturing a coil apparatus may further comprise the step of fixing the core members either directly or indirectly via the core-coupling unit to the electronic-part-mounting substrate by using a fixing unit after the step of rubbing the top core member and the bottom core member against each other.
According to the present invention, the core-coupling unit includes the top cover and the bottom cover. A pair of the core members can be coupled with each other by being clamped by the top cover and the bottom cover coupling with each other. Therefore, the clamping force of the core-coupling unit to be applied to the core members is small compared with the known coil apparatus.
Since the core-coupling unit including the top cover and the bottom cover is provided with the backward-forward-core-position-restricting unit and the backward-forward-movement-allowing unit, the top cover and the bottom cover can be moved backward and forward relative to each other when the core members are clamped by using the anti-removal unit, and the top core member and the bottom core member can be moved backward and forward relative to each other and together with the top cover and the bottom cover, respectively, whereby core-rubbing can be performed by applying only a small force. Therefore, the core-rubbing can be performed efficiently.
As described above, the pair of core members can be moved backward and forward relative to each other by applying a small force, thereby performing core-rubbing. Therefore, a risk of breakage of the core members during core-rubbing can be suppressed even when the core members are made thin, whereby the core members can be made thin and reduction in thickness of the coil apparatus can be advanced.
When the anti-removal unit is formed with the apertures and the projections, and the play-gaps between each projection and the front and rear edges of the aperture, are formed as a backward-forward-movement-allowing unit, the top cover and the bottom cover can be moved backward and forward relative to each other when the legs of the top cover and the bottom cover couple with each other in a very simple configuration.
When cut-away parts are formed in the legs of at least one of the top cover and the bottom cover, and inclined faces are formed on the projections of the anti-removal unit, on which inclined faces the edges of the apertures climb when the top cover and the bottom cover move backward and forward relative to each other, the amount of movement of the top cover and the bottom cover relative to each other can be maintained by the cut-away parts and the inclined faces of the projections even when the play-gaps between the edges of each aperture and the projection are reduced so as to facilitate positioning of the top cover and the bottom cover.
With the above-described arrangement, the pair of core members can be coupled with each other without variations in position, core-rubbing can be efficiently performed, and the pair of core members can be reliably brought into close contact with each other, whereby deterioration of the characteristics of the coil apparatus can be avoided, and a highly reliable coil apparatus can be provided.
When the position-restricting unit which restricts the positions of the core members in the backward and forward directions is formed by the lips provided at the front ends and the rear ends, respectively, of base plates of the top cover and the bottom cover, respectively, the positions of the core members can be restricted by a simple structure.
When a fixing unit which fixes the core members to the electronic-part-mounting substrate is provided, the displacement of the core members during, for example, transportation of the electronic-part-mounting substrate after the process of core-rubbing can be reliably avoided by fixing the core members to the electronic-part-mounting substrate by using the fixing unit, whereby reliability of the characteristics of the coil apparatus can be further improved.
When the fixing unit is formed with a bonding material having a resin, the core members can be easily fixed to the electronic-part-mounting substrate by using the bonding material which can be obtained at a low cost, thereby preventing the cost of the coil apparatus from increasing.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.